1. Field of the Invention
This invention relates to extension ladders. More particulary, it concerns extension ladders with automatic hook locks for length adjustment combined with housing bars and an adjacent rung thereby avoiding the hazard of a skipped rung.
2. Description of the Prior Act
It is conventional practice in the manufacture of extension ladders to use automatic hook locks of the tension type to enable the position of the fly section of the ladder to be varied relative to the bed section. Such hook locks can be compact, safe and durable with low maintenance requirements, except an occasional lubrication. They are conveniently adaptable to positive spring biasing toward a locking position providing a dependable positioning arrangement when the fly section is placed behind the bed section, which in turn contributes to safety and convenience in use of the ladder.
Such hook locks also maybe used with the fly section in front of the bed section, but the conventional omission of one rung (a skipped rung) in the fly section to provide space for the hook locks to operate creates a safety hazard and diminishes the convenience and ease of use of the ladder.
The safety hazard created by a skipped rung in the fly section of an extension ladder is particularly serious when the fly section is used separately from the bed section as a separate straight ladder. This has resulted in enactment of regulations requiring that extension ladders with a skipped rung be equipped with positive stops to prevent disassembly of the fly section from the bed section.
The problems associated with extension ladders having a skipped rung have been long recognized and ladders have been designed to allow extension ladders to have automatic locking devices without need for a skipped rung (see U.S. Pat. Nos. 968,040 and 1,457,100). However, ladder constructions that require highly specialized hooks or that limit the extent of movement of the locks are not generally accepted by ladder manufactures or ladder users. Even though there have been prior art extension ladders without skipped rungs, most extension ladders currently available with automatic hook locks do involve a skipped rung in the fly section. Hence, improvements in the construction of extension ladders are needed to eliminate skipped rungs in the fly section and, at the same time, provide ladders that are strong, safe, and easy to use while being acceptable to both ladder manufacturers and users.